candid 0.9.1

Candid is an interface description language (IDL) for interacting with canisters running on the Internet Computer.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233

use super::internal::{find_type, Field, Label, Type, TypeInner};
use crate::bindings::candid::pp_args;
use crate::types::TypeEnv;
use crate::{Error, Result};
use anyhow::Context;
use std::collections::{HashMap, HashSet};

pub type Gamma = HashSet<(Type, Type)>;

/// Check if t1 <: t2
pub fn subtype(gamma: &mut Gamma, env: &TypeEnv, t1: &Type, t2: &Type) -> Result<()> {
    use TypeInner::*;
    if t1 == t2 {
        return Ok(());
    }
    if matches!(t1.as_ref(), Var(_) | Knot(_)) || matches!(t2.as_ref(), Var(_) | Knot(_)) {
        if !gamma.insert((t1.clone(), t2.clone())) {
            return Ok(());
        }
        let res = match (t1.as_ref(), t2.as_ref()) {
            (Var(id), _) => subtype(gamma, env, env.rec_find_type(id).unwrap(), t2),
            (_, Var(id)) => subtype(gamma, env, t1, env.rec_find_type(id).unwrap()),
            (Knot(id), _) => subtype(gamma, env, &find_type(id).unwrap(), t2),
            (_, Knot(id)) => subtype(gamma, env, t1, &find_type(id).unwrap()),
            (_, _) => unreachable!(),
        };
        if res.is_err() {
            gamma.remove(&(t1.clone(), t2.clone()));
        }
        return res;
    }
    match (t1.as_ref(), t2.as_ref()) {
        (_, Reserved) => Ok(()),
        (Empty, _) => Ok(()),
        (Nat, Int) => Ok(()),
        (Vec(ty1), Vec(ty2)) => subtype(gamma, env, ty1, ty2),
        (Null, Opt(_)) => Ok(()),
        (Opt(ty1), Opt(ty2)) if subtype(gamma, env, ty1, ty2).is_ok() => Ok(()),
        (_, Opt(ty2))
            if subtype(gamma, env, t1, ty2).is_ok()
                && !matches!(env.trace_type(ty2)?.as_ref(), Null | Reserved | Opt(_)) =>
        {
            Ok(())
        }
        (_, Opt(_)) => {
            #[cfg(not(feature = "mute_warnings"))]
            eprintln!("FIX ME! {t1} <: {t2} via special opt rule.\nThis means the sender and receiver type has diverged, and can cause data loss.");
            Ok(())
        }
        (Record(fs1), Record(fs2)) => {
            let fields: HashMap<_, _> = fs1.iter().map(|Field { id, ty }| (id, ty)).collect();
            for Field { id, ty: ty2 } in fs2.iter() {
                match fields.get(id) {
                    Some(ty1) => subtype(gamma, env, ty1, ty2).with_context(|| format!("Record field {id}: {ty1} is not a subtype of {ty2}"))?,
                    None => subtype(gamma, env, &Opt(Empty.into()).into(), ty2).map_err(|_| anyhow::anyhow!("Record field {id}: {ty2} is only in the expected type and is not of opt or reserved type"))?,
                }
            }
            Ok(())
        }
        (Variant(fs1), Variant(fs2)) => {
            let fields: HashMap<_, _> = fs2.iter().map(|Field { id, ty }| (id, ty)).collect();
            for Field { id, ty: ty1 } in fs1.iter() {
                match fields.get(id) {
                    Some(ty2) => subtype(gamma, env, ty1, ty2).with_context(|| {
                        format!("Variant field {id}: {ty1} is not a subtype of {ty2}")
                    })?,
                    None => {
                        return Err(Error::msg(format!(
                            "Variant field {id} not found in the expected type"
                        )))
                    }
                }
            }
            Ok(())
        }
        (Service(ms1), Service(ms2)) => {
            let meths: HashMap<_, _> = ms1.iter().map(|(name, ty)| (name, ty)).collect();
            for (name, ty2) in ms2.iter() {
                match meths.get(name) {
                    Some(ty1) => subtype(gamma, env, ty1, ty2).with_context(|| {
                        format!("Method {name}: {ty1} is not a subtype of {ty2}")
                    })?,
                    None => {
                        return Err(Error::msg(format!(
                            "Method {name} is only in the expected type"
                        )))
                    }
                }
            }
            Ok(())
        }
        (Func(f1), Func(f2)) => {
            if f1.modes != f2.modes {
                return Err(Error::msg("Function mode mismatch"));
            }
            let args1 = to_tuple(&f1.args);
            let args2 = to_tuple(&f2.args);
            let rets1 = to_tuple(&f1.rets);
            let rets2 = to_tuple(&f2.rets);
            subtype(gamma, env, &args2, &args1).context("Subtype fails at function input type")?;
            subtype(gamma, env, &rets1, &rets2).context("Subtype fails at function return type")?;
            Ok(())
        }
        // This only works in the first order case, but service constructor only appears at the top level according to the spec.
        (Class(_, t), _) => subtype(gamma, env, t, t2),
        (_, Class(_, t)) => subtype(gamma, env, t1, t),
        (Unknown, _) => unreachable!(),
        (_, Unknown) => unreachable!(),
        (_, _) => Err(Error::msg(format!("{t1} is not a subtype of {t2}"))),
    }
}

/// Check if t1 and t2 are structurally equalivalent, ignoring the variable naming differences.
/// Note that this is more strict than `t1 <: t2` and `t2 <: t2`, because of the special opt rule.
pub fn equal(gamma: &mut Gamma, env: &TypeEnv, t1: &Type, t2: &Type) -> Result<()> {
    use TypeInner::*;
    if t1 == t2 {
        return Ok(());
    }
    if matches!(t1.as_ref(), Var(_) | Knot(_)) || matches!(t2.as_ref(), Var(_) | Knot(_)) {
        if !gamma.insert((t1.clone(), t2.clone())) {
            return Ok(());
        }
        let res = match (t1.as_ref(), t2.as_ref()) {
            (Var(id), _) => equal(gamma, env, env.rec_find_type(id).unwrap(), t2),
            (_, Var(id)) => equal(gamma, env, t1, env.rec_find_type(id).unwrap()),
            (Knot(id), _) => equal(gamma, env, &find_type(id).unwrap(), t2),
            (_, Knot(id)) => equal(gamma, env, t1, &find_type(id).unwrap()),
            (_, _) => unreachable!(),
        };
        if res.is_err() {
            gamma.remove(&(t1.clone(), t2.clone()));
        }
        return res;
    }
    match (t1.as_ref(), t2.as_ref()) {
        (Opt(ty1), Opt(ty2)) => equal(gamma, env, ty1, ty2),
        (Vec(ty1), Vec(ty2)) => equal(gamma, env, ty1, ty2),
        (Record(fs1), Record(fs2)) | (Variant(fs1), Variant(fs2)) => {
            assert_length(fs1, fs2, |x| x.to_string()).context("Different field length")?;
            for (f1, f2) in fs1.iter().zip(fs2.iter()) {
                if f1.id != f2.id {
                    return Err(Error::msg(format!(
                        "Field name mismatch: {} and {}",
                        f1.id, f2.id
                    )));
                }
                equal(gamma, env, &f1.ty, &f2.ty).context(format!(
                    "Field {} has different types: {} and {}",
                    f1.id, f1.ty, f2.ty
                ))?;
            }
            Ok(())
        }
        (Service(ms1), Service(ms2)) => {
            assert_length(ms1, ms2, |x| format!("method {} : {}", x.0, x.1))
                .context("Different method length")?;
            for (m1, m2) in ms1.iter().zip(ms2.iter()) {
                if m1.0 != m2.0 {
                    return Err(Error::msg(format!(
                        "Method name mismatch: {} and {}",
                        m1.0, m2.0
                    )));
                }
                equal(gamma, env, &m1.1, &m2.1).context(format!(
                    "Method {} has different types: {} and {}",
                    m1.0, m1.1, m2.1
                ))?;
            }
            Ok(())
        }
        (Func(f1), Func(f2)) => {
            if f1.modes != f2.modes {
                return Err(Error::msg("Function mode mismatch"));
            }
            let args1 = to_tuple(&f1.args);
            let args2 = to_tuple(&f2.args);
            let rets1 = to_tuple(&f1.rets);
            let rets2 = to_tuple(&f2.rets);
            equal(gamma, env, &args1, &args2).context("Mismatch in function input type")?;
            equal(gamma, env, &rets1, &rets2).context("Mismatch in function return type")?;
            Ok(())
        }
        (Class(init1, ty1), Class(init2, ty2)) => {
            let init_1 = to_tuple(init1);
            let init_2 = to_tuple(init2);
            equal(gamma, env, &init_1, &init_2).context(format!(
                "Mismatch in init args: {} and {}",
                pp_args(init1).pretty(80),
                pp_args(init2).pretty(80)
            ))?;
            equal(gamma, env, ty1, ty2)
        }
        (Unknown, _) => unreachable!(),
        (_, Unknown) => unreachable!(),
        (_, _) => Err(Error::msg(format!("{t1} is not equal to {t2}"))),
    }
}

fn assert_length<I, F>(left: &[I], right: &[I], display: F) -> Result<()>
where
    F: Fn(&I) -> String,
{
    let l = left.len();
    let r = right.len();
    if l == r {
        return Ok(());
    }
    if l < r {
        Err(Error::msg(format!(
            "Left side is missing {}",
            display(right.last().unwrap())
        )))
    } else {
        Err(Error::msg(format!(
            "Right side is missing {}",
            display(left.last().unwrap())
        )))
    }
}

fn to_tuple(args: &[Type]) -> Type {
    TypeInner::Record(
        args.iter()
            .enumerate()
            .map(|(i, ty)| Field {
                id: Label::Id(i as u32).into(),
                ty: ty.clone(),
            })
            .collect(),
    )
    .into()
}